Compositions comprising mixtures of substituted triarylphosphates

ABSTRACT

COMPOSITIONS COMPRISING MIXTURES OF PHOSPHATE ESTERS HAVING THE GENERAL STRUCTURE   (R-PHENOXY)3-P(=O)   WHEREIN EACH R IS HYDROGEN, AN ALKYL RADICAL, OR AN ARYLALKYL RADICAL WHEREIN THE ARYL IS ATTACHED THROUGH A TERTIARY CARBON ATOM, PROVIDED THAAT AS WITHIN THE TOTAL COMPOSITION, FROM ABOUT 2 TO 45 MOLE PERCENT OF THE TOTAL R GROUPS ARE ALKYL RADICALS HAVING FROM ABOUT 4 TO 18 CARBON ATOMS, FROM 2 TO 45 MOLE PERCENT OF THE TOTAL R GROUPS ARE ALKYL RADICALS WHEREIN THE ALKYL LINKAGE HAS FROM ABOUT 3 TO 13 CARBON ATOMS, AND FROM ABOUT 50 TO 90 MOLE PERCENT OF THE TOTAL R GROUPS ARE HYDROGEN. THE COMPOSITIONS AARE USEFUL AS FUNCTIONAL FLUIDS AND AS COMPONENTS OF FUNCTIONAL FLUID FORMULATIONS.

United States Patent 3,723,315 COMPOSITIONS COMPRISING MIXTURES OF SUBSTITUTED TRIARYLPHOSPHATES James D. Sullivan, Chesterfield, Mo., assignor to Monsanto Company, St. Louis, M0.

N0 Drawing. Continuation-impart of application Ser. No. 110,783, Jan. 28, 1971. This application Mar. 5, 1971, Ser. No. 121,578

Int. Cl. Cm 1/46 US. Cl. 252-49.8 17 Claims ABSTRACT OF THE DISCLOSURE Compositions comprising mixtures of phosphate esters having the general structure wherein each R is hydrogen, an alkyl radical, or an arylalkyl radical wherein the aryl is attached through a tertiary carbon atom, provided that as within the total composition, from about 2 to 45 mole percent of the total R groups are alkyl radicals having from about 4 to 18 carbon atoms, from 2 to 45 molepercent of the total R groups are arylalkyl radicals wherein the alkyl linkage has from about 3 to 13 carbon atoms, and from about 50 to 90 mole percent of the total R groups are hydrogen. The compositions are useful as functional fluids and as components of functional fluid formulations.

CROSS-REFERENCE TO RELATED APPLICATION This application is a continuation-in-part of Ser. No. 110,783 filed Jan. 28, 1971.

BACKGROUND OF THE INVENTION Field of the invention This invention relates to phosphate esters useful as functional fluids and particularly to mixtures of triaryl phosphates wherein the aryl groups are phenyl, alkyl substituted phenyl, and arylalkyl substituted phenyls.

DESCRIPTION OF PRIOR ART Phosphate esters have long been used as functional fluids such as hydraulic fluids, lubricants and the like. They have been used alone in wholly synthetic compositions and as additives to mineral oil compositions to impart extreme pressure properties thereto.

Neutral phosphate esters comprise three classes of compounds: trialkyl phosphates, triaryl and alkyl substituted triaryl phosphates, and mixed alkylaryl phosphates. Of

these, the triaryl phosphates are generally known for their thermal stability, low vapor pressure, lack of odor, 10W reactivity and low flammability. Such properties are required in lubricants intended for high temperature industrial and aircraft applications. Unfortunately, the triaryl phosphates are not acceptable as lubricants per se because of poor lubricity and viscosity characteristics. Phosphate esters which have good lubricity and viscosities, notably the trialkyl phosphates and the alkldiaryl phosphates, are generally unsuitable for high temperature applications because of poor oxidative stability. Thus it is common to formulate mixtures of esters in an effort to arrive at a balance of desirable properties.

In recent years there has been a steady increase in the severity of operating conditions in industrial equipment as well as in aircraft, rockets, and the like. As a consequence of this activity, there has been increased demand for synthetic lubricants and hydraulic fluids which have good viscosity, lubricity and load-carrying ability, and which are able to resist oxidative and thermal degradation. The efforts of the prior art to provide such fluids have been directed primarily toward blending selected phosphate esters and incorporating a variety of additives such as lubricity agents, V.I. improvers, oxidation inhibitors, and the like. Alkyl substituted triaryl phosphates, such as trixylenyl phosphate have been of interest since it is known that the presence of alkyl carbons imparts lubricity to the ester. However, since the alkyl carbons also render the ester less oxidatively stable, alkyl substituted triaryl phosphates have been generally unsuited for use where oxidative stability was required. Although some improvement in lubricity and oxidative stability of conventional phosphate esters can be attained through the use of additives as taught by the prior art, a need exists for a phosphate ester composition which inherently possesses these desirable properties.

SUMMARY It is an object of the present invention to provide compositions useful as functional fluids and as components of functional fluids comprising triaryl phosphate esters which possess a combination of superior properties required by modern industrial applications. It is a further object of this invention to provide mixtures of substituted triaryl phosphates including alkyl substituted compounds which have good lubricity and which are superior to known alkyl substituted triaryl phosphates in thermal and oxidative stability.

The compositions of the present invention are comprised of mixtures of triaryl phosphates having the general structure wherein each R is hydrogen, an alkyl radical of 6 to 18 carbon atoms, or an arylalkyl radical having the general structure wherein R is an alkyl of 1 to about 6 carbon atoms; provided that as within the total composition, from about 2 to 45 mole percent of the total R groups are alkyl radicals, from 2 to 45 mole percent of the R groups are arylalkyl radicals, and from about 50 to 90 mole percent of the total R groups are hydrogen.

These compositions are prepared by the reaction of phenols and selected substituted phenols with phosphorus oxychloride in accordance with conventional procedures and the following equation:

In accordance with the present invention, the phenols used in the above reaction may be a mixture of phenol and substituted phenols combined in proportions to provide the particular substituted triaryl phosphates encompassed by this invention. Alternatively, individual phosphate esters can be prepared from specific phenols and substituted phenols and these esters can be blended to provide the compositions of this invention.

These phosphate ester mixtures have good lubricity, are resistant to oxidation, and are particularly useful as lubricating and pressure transmitting functional fluids.

DESCRIPTION OF PREFERRED EMBODIMENTS The triaryl phosphate esters of this invention are readily prepared using conventional methods of the prior art. It is known, for example, that cyclic alcohol esters of phosphoric acid can be prepared by reacting an alcohol or mixture of alcohols with phosphorus oxyhalide at temperatures of from about to 300 C. The reactions are carried out by heating a mixture of the selected reactants to a reaction temperature, preferably in the presence of a catalyst such as metallic calcium, magnesium or aluminum or a chloride of magnesium, aluminum, iron or tin, etc. The temperature to which the mixture must be heated in order to obtain rapid reaction is of course dependent upon the particular reactants employed, the relative proportions of the reactants, the presence or absence of a catalyst, etc. However, since the reaction is accompanied by evolution of hydrogen halide, it is necessary merely to heat the mixture to a temperature at which hydrogen halide gas is evolved. The reactions are preferably carried out at the lowest convenient reaction temperature, usually below 300 C. and preferably between 120-220 C.

The phosphorus oxyhalide reactant can be phosphorus oxychloride or phosphorus oxybromide. The alcohol can be a. phenol or substituted phenol or an alkali metal salt of such phenols.

Mixed triaryl phosphate esters can be prepared by reacting phenols and substituted phenols individually with phosphorus oxyhalide in a series of separate reactions, or by reacting a mixture of such phenols and substituted phenols simultaneously in a single reaction. In the first instance, substituted phenols are reacted with phosphorus oxyhalide to form monoaryl phosphoric acid dihalides or diaryl phosphoric acid monohalides which are subsequently reacted with phenol to complete esterification. In such a system it is preferable, in formation of the intermediate aryl phosphoric acid halide, to employ the substituted phenol in a proportion slightly lower than that theoretically required since the yield of such intermediate product is generally highest when this is done. It is also desirable although not necessary to purify the intermediate aryl phosphoric acid halide product by distillation or otherwise before completing the reaction with phenol since the desired mixed triaryl phosphate product is thereby obtained in maximum yield and purity.

The preparation of mixed triaryl phosphates by the simultaneous reaction of a mixture of different substituted phenols and phenol is preferred whenever possible for reasons of simplicity and economics. The phenols are mixed in proportions calculated to provide the desired concentrations of the particular phenol substitutents in the final ester product. Although this technique necessarily produces an undefined mixture of specific triaryl phosphate esters, the properties of the product can be predicted and controlled by the relative molar ratios of the selected phenyl substituents, and the products are well suited for use as functional fluids. After the esterification reaction is completed, the hot reaction mixture may be blown with air or nitrogen or placed under vacuum to remove hydrogen halide and other volatile impurities.

The essential elements of the triaryl phosphate esters of this invention are the phenol substituents previously identified as alkyls of 4 to 18 carbon atoms and groups. I have found that the fluid properties of oxidative stability, viscosity, lubricity and autogenous ignition temperature (AIT) can be controlled and optimized to yield a particularly desirable fiuid by properly balancing the relative proportions of these elements.

In particular, I have found that as the proportion of -C(R) in the ester product is increased, the oxidative stability and viscosity of the fluid are increased, and that as the proportion of the alkyl ingredient is increased, fluid lubricity is increased and an intermediate viscosity is supported. As the proportions of both alkyl and C(R') groups are decreased, the viscosity of the fluid is decreased and the AIT level is increased.

Thus by proper selection of the relative proportions of the phenol, alkyl substituted phenol, and C(R') substituted phenol reactants, it is possible to construct a triaryl phosphate fluid having a wide range of desirable properties.

Surprisingly, the compositions of the present invention have far greater oxidative stability than would be predicted on the basis of the number of alkyl carbons in the structure. The presence of alkyl carbons in triaryl phosphates is known to enhance fluid lubricity, but also to render the compositions more susceptible to oxidation. Thus it can be shown that the oxidation resistance of alkyl substituted triphenyl phosphates varies inversely with the number of alkyl carbons present in the structure and that trixylenyl phosphate, for example, is less stable than triphenyl cresyl phosphate which in turn is less stable than triphenyl phosphate. A preferred composition of the present invention has an average of five alkyl carbons per ester and comprises a mixture of two parts cumylphenyl diphenyl phosphate and one part nonylphenyl diphenyl phosphate. The superior oxidative stability of this composition as compared with other alkyl substituted triphenyl phosphates of comparable alkyl content is illustrated by the data in Table I which were obtained by standard Oxidation and Corrosion test hereinafter defined. Good oxidative stability is indicated by low viscosity increase, low metal attack, and no coke or sludge formation.

TABLE I Oxidation and corrosion test Percent viscosity increase No. of Corrosion,

Phosphate ester alkyl 100 F. 210 F. Cu, mg./cm.* Coking Sludge 1 Triphenyl phosphate 0 0 -0. 56 None--." None. 2 Gresyl diphenyl phosphate. 1 18. 4 3 1. 7 -..do Light. 3 Xylenyl diphenyl phosphate 2 Heavy Heavy; 4 Tncresyl phosphate 3 36. 5 20. 5 0. 9 Medium. Do. 5 Trixylenyl phosphate 6 Heavy Do. 6 cumylphenyl diphenyl P...} 4 5 15. 3 0. 4 N one..- None.

% nonylphenyl diphenyl P 1 Solid at 100 F.

i No measurement due to heavy sludge and coke level; N o measurement-solid immobile tar at 100 F.

4 Average Corrosion rate for Mg, Al, Cd, and Fe not significant.

The properties of any particular triaryl phosphate composition will depend to a great extent on the nature of the R and R groups as well as on their relative proportions in the fluid. Consequently, the size of the R and R groups must be taken into consideration in determining the proportions of the substituted phenol reactants to be employed in the preparation of the ester.

As previously described, the R radicals in the substituent can be alkyls of from 1 to about 6 carbon atoms and preferably are alkyls of from 1 to about 3 carbon atoms. The R group of the alkyl substituted phenol can be from about 4 to 18 carbon atoms, and preferably is from about 6 to 12 carbon atoms. The variations permissible in the selection of these alkyl groups provides for a multiplicity of combinations and makes it impractical to attempt to define all combinations in terms of concentration of substituents and properties of the ester product. Such determination can however be easily made without undue experimentation by those skilled in the art for any particular combination of substituted phenol reactants which are of interest. The determination is assisted by the fact that there are certain limitations on the relative proportions of the phenol substituents. Specifically, the preferred triaryl phosphate esters of this invention are triphenyl phosphates in which from about 2 to 45 mole percent of the phenyls are alkyl substituted, from about 2 to 45 mole percent of the phenyls are arylalkyl substituted, and from about 50 to 90 mole percent of the phenyls are unsubstituted.

For purposes of illustration, the following examples are provided to demonstrate a preferred embodiment of this invention. In these examples, the arylalkyl substituent is cumyl, the R in C(R') substituent being methyl, and the alkyl substituent is nonyl. The ratio of reactants is controlled to yield an ester product comprising nominally two parts cumylphenyl disphenyl phosphate and one part nonylphenyl diphenyl phosphate.

In preparing this product it is desirable to carry out a two-stage reaction wherein one mole nonylphenol and two moles cumylphenol are reacted first with three moles phosphorus oxychloride to yield a mixture of monoaryl phosphoric acid dichloridates, which are subsequently reacted With phenol to complete the esterification. The nonylphenol and cumylphenol can be mixed and reacted simultaneously with good results. Alternatively, the reactions to form the dichloridates can be carried out separtely, and the partial ester products combined either prior to or after the esterification is completed by reaction with phenol.

If desired, the improved fluids of this invention may be prepared by reacting a mixture comprising two moles of cumylphenol, one mole of nonylphenol and six moles of phenol with three moles of phosphorus oxychloride. The product by this reaction is conveniently referred to by its nominal composition of two parts cumylphenyl diphenyl phosphate and one part nonylphenyl diphenyl phosphate while recognizing that the product in fact contains other esters such as di(nonylphenyl)phenyl phosphate, di- (cumylphenyl)phenyl phosphate, cumylphenyl nonylp llienyl phenyl phosphate, triphenyl phosphate and the To the above reaction product may be added additional amounts of triphenyl phosphate as desired to decrease the relative proportions of the cumylphenyl and nonyl substituents in the fluid and thereby decrease the viscosity and increase the AIT of the fluid.

The following example describes the preparation of a preferred composition comprising two parts cumylphenyl diphenyl phosphate and one part nonylphenyl diphenyl phosphate. The example is provided for purposes of illustration only and is not intended to limit the scope of this invention.

EXAMPLE To a reactor equipped with a stirrer, a refrigerated condensing system and a subsurface feed-line are added 19.3 pounds of nonylphenol and 37.2 pounds of cumylphenol. The mixture of phenols is heated to about C. and 0.56 pound of magnesium chloride catalyst is added thereto. A phosphorus oxychloride charge of 40.3 pounds is slowly added to the stirred phenol-catalyst mixture through the subsurface feed-line. Heat is supplied to the reactor to maintain a reaction temperature of about 100 C.

When the addition of phosphorus oxychloride is completed, the reactor is heated to C. and held at that temperature for one hour. The pressure is then slowly reduced to 80-100 mm. and the reactor maintained at this pressure for about one hour to complete the reaction and formation of nonylphenyl phosphorodichloridate and cumylphenyl phosphorodichloridate, and to remove HCl byproduct from the reaction mass.

The reactor is then restored to atmospheric pressure and 54.5 pounds of phenol is slowly added through the subsurface feed-line while the reactor contents are maintained at about 125 C. After the addition of phenol is complete, the reactor is heated to C. and held at this temperature for about one hour. The pressure of the reactor is then slowly reduced to 20-30 mm. and after a one hour hold period the temperature is increased to C. while maintaining a reduced pressure, and held at these conditions for an additional one hour.

At this point the reactor is restored to atmospheric conditions and 0.56 pound of magnesium chloride catalyst is added to the reactor with stirring. After addition of this catalyst charge is complete, the reactor pressure is again reduced to 20-30 mm. at 160 C. and the reactor is held at these conditions for about two hours to complete the esterification reaction and remove gaseous HCI reaction product.

The product of the esterification reaction is recovered as a clear, pale yellow mixture comprising one part nonylphenyl diphenyl phosphate and two parts cumylphenyl diphenyl phosphate.

TABLE II including alkylene polymers, alkylene oxide type polymers, alkyl benzenes, dialkyl benzenes, polyphenyls, halogenated benzenes, halogenated alkyl benzenes, halogenated biphenyl, monohalogenated diphenyl ethers, trialkyl phosphine oxides, diaryl alkyl phosphonates, trialkyl phosphonates, aryl dialkyl phosphonates, triaryl phosphonates, triaryl phosphates, trialkyl phosphates, and mixed arylalkyl phosphates.

O and Test Composition: R, moi percent Viscosity, Percent vis. Corrosion Wear cs. at increase Cu, A I.T., test, scar Fluid Nonyl Oumyl Hydrogen 100 F. at 100 F. rug/em. F. dia., mm.

4. 8 28. 66. 6 151 18. 0 0. 01 915 0. 80 11. 1 22. 2 66. 6 125 16. 0 0. 04 905 0.70 18. 3 15. 0 66. 6 108 865 0. 77 26. 5 6. 8 66. 6 88 47. 9 -0. 69 855 0. 70 19. 8 5. 0 75. 2 49 1, 050 0. 73 8. 4 16. 8 74. 8 65 U) U) U) 7. 2 14. 3 78. 5 50 9 U) Not determined.

Mg, Al, Cd, and Fe corrosion rates not significant.

In the above table, Fluid E was prepared by adding triphenyl phosphate to the composition of Fluid D and Fluids F and G were prepared by adding different amounts of triphenyl phosphate to the composition of Fluid B.

Oxidation and Corrosion test (0&0) was conducted according to Federal Test Method Standard 791-Meth0d 5308.4 with the following modifications:

Temperature-350 F.

Timel68 hours Air rate-10 liters (dry) Metals-Cu, Mg, Al, Cd, Fe

Metal Coupons-Attached to glass rod Wear Test data was obtained according to the conventional Shell 4-ball test operated at 625 r.p.m. under a 40 kg. load at 167 F. for one hour.

Autogenous Ignition Temperature (AIT) was determined by ASTM D-2l55-66.

The data of Table II illustrates the desirable performance properties obtained with the compositions of this invention. Specifically, it is seen that oxidative stability as determined by percent viscosity increase and copper corrosion rate is generally good. Lubricity of the compositions defined in Table II is also very good as evidenced by the Wear Test data wherein all scar diameters were less than 1 mm. Particularly significant is the small scar diameter obtained in Fluid E, which illustrates the excellent lubricity obtained with the compositions of this invention even at low levels of viscosity.

In formulating functional fluids, the compositions of this invention can also contain dyes, pour point depressants, metal deactivators, acid scavengers, antioxidants, defoamers, viscosity index improvers, lubricity agents, diluents, and the like. Such additives for use in phosphate ester based functional fluid formulations are commonly used and are well known in the art.

It is also within the scope of this invention that the substituted triaryl phosphate base stocks, as aforedescribed, can be utilized singly or as fluid compositions containing two or more base stocks in varying proportions. The base stocks can also contain other fluids which include, in addition to the compositions of this invention, fluids derived from petroleum and other synthetic fluids Mixtures of the compositions to this invention with one or more other fluid compositions are useful in formulating functional fluids having one or more specific physical properties such as, for example, low fluid viscosity which may be required for a particular application. Other fluid compositions useful in formulating such functional fluids include phosphate esters such as cresyl diphenyl phosphate, butyl diphenyl phosphate, dibutyl phenyl phosphate, tributyl phosphate and trixylyl phosphate; amides of an acid of phosphorus including alkyl phosphoroamidates and alkyl phosphoroamidates; polyesters such as the esters of pentaeiythritol, dipentaerythritol, and trimetholyl propane; carboxylic acid esters including dimeric and trimeric polycarboxylic acid esters; organo-orthosilicates, alkoxypolysiloxanes, and organopolysiloxanes such as dimethylpolysiloxane, methylphenylpolysiloxane, methylchlorophenylpolysiloxane, and methyltrifluoropropylpolysiloxane; aryl ethers and thioethers including bis(phenoxyphenyl)ether, bis(phenoxyphenoxy)benzene, bis (phenoxyphenoxyphenyl) benzene, 2-phenylmercapto-4'-phenoxy diphenyl sulfide, o-bis (phenylmercapto benzene, phenylmercaptobiphenyl, chlorophenylmercaptobenzene, bis-(alkylphenylmercapto)diphenyl ether, and trisphenylmercaptobenzene; monoand dialkyl thiophenes such as 2,5 l-hexyll-methylnonyl) thiophene, Z-tert-butyl thiophene, 2,5 l-propylcyclobutyl) thiophene, 2,4-( l-methylcyclopentyl thiophene, and 2,4- l-n-dodecylpentyl thiophene;

halogenated aromatic hydrocarbons such as the halodiphenyl ethers, halobenzenes, haloalkylbenzenes, halonaphthylenes, and halogenated polyphenyls; and petroleum derived hydrocarbon oils.

When formulating functional fluid compositions for specific uses, the compositions of this invention can constitute either a major or a minor part of the total composition. In other words, it is within the scope of the present invention not only to add other materials to the compositions disclosed herein in order to modify the properties of these compositions, but also to add the compositions of the present invention to functional fluids comprising a major proportion of some other fluid base stock in order to modify the properties of such base stock. Such formulations are illustrated by the following two examples -which are presented for purposes of illustration only and are not limiting in any respect.

Fluid H.Viscosity, 30 cs. 100 F.:

70% of triaryl phosphate comprising 1 part nonylphenyl diphenyl phosphate 2 parts cumylphenyl diphenyl phosphate 3 parts triphenyl phosphate 30% cresyl diphenyl phosphate Fluid J.Viscosity, 30 cs. 100 F.:

29% of triaryl phosphate comprising 1 part nonylphenyl diphenyl phosphate 2 parts cumylphenyl diphenyl phosphate 68.4%. cresyl diphenyl phosphate 2.6% tributyl phosphate Both of the above fluids are found to have good lubricity and good oxidation stability. Fluids H and I illustrate formulations where the compositions of this invention are present as a major ingredient and as a minor ingredient respectively. Although in most instances the compositions of this invention will be present in amounts of at least about 20 percent by weight of the total fluid, the amount may be only percent or less in some fluid formulations.

The preceding examples and data are provided by way of illustration only and are not intended to be limiting of the invention. Other substituted triaryl phosphates besides those specifically described which are useful as functional fluids will be apparent to those skilled in the art in view of this disclosure, and such compositions are accordingly included within the scope of the invention.

The embodiments in which an exclusive property or privilege is claimed are defined as follows:

1. A composition consisting essentially of a mixture of phosphate esters having the general structure wherein each R is hydrogen, an alkyl radical, or an arylalkyl radical wherein the aryl is attached through a tertiary carbon atom of the alkyl linkage, provided that of the total R groups in the mixture, from 2 to 45 mole percent are alkyl radicals having from about 4 to 18 carbon atoms, from '2 to 45 mole percent are arylalkyl radicals wherein the alkyl linkage has from 3 to about 13 carbon atoms, and from about 50 to 90 mole percent are hydrogen.

2. A composition of claim 1 wherein the -R groups which are alkyl radicals have from about 6 to 12 carbon atoms, and the R groups which are arylalkyl radicals have an alkyl linkage of from 3 to about 7 carbon atoms.

3. A composition of claim 2 wherein the alkyl radicals are nonyl and arylalkyl radicals are cumyl.

4. A composition of claim 2 comprising a mixture of cumylphenyl diphenyl phosphate and nonylphenyl diphenyl phosphate.

5. A composition of claim 4 wherein the molar ratio of cumylphenyl diphenyl phosphate to nonylphenyl diphenyl phosphate is about 2 to l.

6. A composition of claim 2 comprising a mixture of cumylphenyl diphenyl phosphate, nonylphenyl diphenyl phosphate, and triphenyl phosphate.

7. A composition of claim 6 wherein the molar ratio of cumylphenyl diphenyl phosphate to nonylphenyl diphenyl phosphate is about 2 to 1. i

8. A composition comprising a mixture of phosphate esters of claim 1 and at least one other fluid composition useful in formulating functional fluids.

9. A composition of claim 8 wherein said other fluid composition is selected from the group consisting of phosphate esters, amides of an acid of phosphorus, polyesters, carboxylic acid esters, organo-orthosilicates, alkoxypolysiloxanes, organopolysiloxanes, aryl ethers and thioethers, monoand dialkyl thiophenes, halogenated aromatic hydrocarbons, and petroleum derived hydrocarbon oils.

10. A composition comprising a mixture of phosphate esters of claim 4 and at least one other fluid composition useful in formulating functional fluids.

11. A composition of claim 10 comprising a mixture of cumylphenyl diphenyl phosphate, nonylphenyl diphenyl phosphate, and cresyl diphenyl phosphate.

12. A composition comprising a mixture of phosphate esters of claim 6 and at least one other fluid composition useful in formulating functional fluids.

13. A composition of claim 12 comprising a mixture of cumylphenyl diphenyl phosphate, nonylphenyl diphenyl phosphate, triphenyl phosphate and cresyl diphenyl phosphate.

14. In a method of operating a hydraulic pressure device wherein a displaceable force is transmitted to a transplaceable member by means of a hydraulic fluid the improvement which comprises employing as saidfluid a composition of claim 1.

15. In a method of operating a hydraulic pressure device wherein a displaceable force is transmitted to a transplaceable member by means of a hydraulic fluid the improvement which comprises employing as said fluid a composition of claim 8.

16. In a method of lubricating metal surfaces in frictional contact wherein a lubricating composition is interposed between the surfaces, the improvement which comprises employing as said lubricating composition a composition of claim 1.

17. In a method of lubricating metal surfaces in frictional contact wherein a lubricating composition is interposed between the surfaces, the improvement which comprises employing as said lubricating composition a composition of claim 8.

References Cited UNITED STATES PATENTS 3,012,057 12/1961 Fierce et a1. 252-498 X 2,995,519 8/1961 Shatynski et al. 260-966 X 3,071,549 1/1963 Stark 252-498 X DANIEL E. WYMAN, Primary Examiner W. H. CANNON, Assistant Examiner U.S. Cl. X.R. 252-78 

